Process for producing synthetic linear aromatic sulfur-containing condensation polyesters and products thereof



United States PROCESS FOR PRODUCING SYNTHETIC LINEAR AROMATICSULFUR-CONTAINING CONDENSA- TION POLYESTERS AND PRODUCTS THEREOF GeorgeE. Ham, Decatur, Ala, assignor to The Chemstrand Corporation, Decatur,Ala., a corporation of Delaware No Drawing. Application December 13,1954 Serial No. 474,985

16 Claims. (Cl. 260-784) The simplest form of polymer containing esterlinkages is the polyester and it is well-known that linear polyesterscan be made from dibasic acids and glycols. When these polyesters are ina highly polymerized condition, they can be formed into filaments,fibers, and the like, which can be permanently oriented by cold drawing.That is, when the esterification reaction is carried out for asufiiciently prolonged period under conditions such as to remove thewater of reaction effectively, linear polyesters may be produced havingextremely high molecular weights, which, in the case of polyesterscapable of crystallizing at ordinary temperatures, may possess theproperty of cold drawing. The non-crystalline polyesters of highmolecular weight are viscous liquids at ordinary temperatures whereasthe crystallizable polyesters are hard, tough, microcrystallinesubstances which melt at a definite crystalline melting point to formviscous liquids.

When preparing a polyester from a dibasic acid and a glycol the reactiontakes place in two stages. In the first stage an intermediate product isformed which is an hydroxyalkyl derivative of the dibasic acid and Wateris evolved. In the second stage a simple molecule, such as water orglycol, is evolved forming the polyester. High temperatures arenecessary to effect the first stage of the reaction and the reactionmass must be maintained at these elevated temperatures for considerablelengths of time. These factors have led to discoloration of thepolyester, which obviously is undesirable when producing filaments andfibers forcommercial use. In addition, the prolonged periods of timenecessary to effect reaction are not conducive to continuous production,which is desirable when operating on a commercial scale.

Accordingly, it is an object of the present invention to provide a newand improved process for producing synthetic linear condensationpolyesters which are capable of being formed into filaments, fibers, andthe like, and which, when cold drawn, show permanent orientation alongthe fiber axis, as revealed by characteristic X-ray patterns. It isanother object of the invention to provide a new and improved processfor producing synthetic linear condensation polyesters which results ina reduction of time in which reaction takes place. It is still anotherobject of the invention to provide a new and improved process forproducing synthetic linear condensation polyesters which is moreeconomical than prior processes and which is conducive to continuousoperation.

It is a still further object of the invention to provide atent PatentedJan. 20, 1959 new and improved synthetic linear condensation polyesters.Other objects and advantages of the present invention. will be apparentfrom the description thereof hereinafter.

It has unexpectedly been found that the disadvantages of prior artmethods can be overcome and the objects of the present invention can, ingeneral be accomplished, by replacing the glycol with an alkylenesulfite. For example, ethylene sulfite or propylene sulfite may besuccessfully employed in the practice of the present invention.

In the preparation of synthetic linear condensation polyesters from adibasic acid and a glycol, the dibasic acid and glycol are mixedtogether and heated in the presence or absence of esterificationcatalysts, as desired. It is necessary to employ at least about onemolecular proportion of the glycol per molecular proportion of dibasicacid. Generally, however, higher proportions of the glycol relative tothe dibasic acid are used. For example, up to five moles of glycol permole of dibasic acid are employed because by so doing the initialesterification is said to take place more readily. However, even at thisupper ratio of 5 moles glycol per mole of dibasic acid the time isprohibitive for continuous operation since a minimum of 7 to 8 hours isnecessary to complete the first or initial esterification reactionwhereby the glycol ester of the dibasic acid is formed. However, whenemploying an alkylene sulfite in place of the glycol the time foreffecting the initialv esterification is considerably reduced. It hasbeen found that in the process of the present invention, the dibasicacid and alkylene sulfite may be employed in the following ratio: onemole of dibasic acid to 1 to 9 moles of alkylene sulfite.

During the first stage of the-reaction (initial esterification to formthe glycol ester) the temperature approaches the boiling point ofglycol. When all of the acid has reacted with the sulfite, thetemperature is increased. The residue is then further heated above itsmelting point. This is known as the second stage and the one in whichcondensation takes place forming the linear condensation polyester. Itis to be noted, however, that the polyester may be formed in one stage.That is, when a clear solution is first formed it contains the polymerand further heating may be minimized or eliminated. This accounts forthe great saving in time of reaction, noted in more detail hereinafter.

During the second stage, glycol is liberated and the melting point andthe viscosity of the reaction mixture gradually increases. The heatingis continued until the melt produced has cold-drawing properties, i.e'., filaments formed from the melt are capable of being cold drawn. Theheating may be carried out at atmospheric or sub-atmospheric pressures,and preferably in an inert atmosphere'in the absence of anoxygen-containing gas. This may be accomplished by bubbling an inertgas, such as nitrogen, through the molten mass. Any inert gas may beemployed.

The glycolliberated in the second stage must be removed which in turnmeans maintaining the reaction mixture or molten mass at elevatedtemperatures for prolonged periods of time. This prolonged heating tendsto discolor the resultant polyester which is obviously undesirable froma commerciaf standpoint. However, when employing an alkylene sulfite inplace of the glycol, proportionately smaller quantities may be employedthan glycol and still achieve the same beneficial properties in theresultant polyester which means a smaller amount of glycol formed. Thisin turn necessitates the removal of less glycol which shortens theperiod of heating thus alleviating the danger of discoloration of theproduct.

During, the first stage of the reaction, wherein the hydroxyalkyl esterof the dibasic acid is formed, no inert solvent medium is employed.Therefore, mixing of solid dibasic acid with glycol has presented aproblem heretofore. When employing an alkylene sulfite, sulfur dioxideis evolved which, when bubbling through the reaction mass, stirs thesame. This is an additional physical advantage of the instant process.

In the practice of the present invention aromatic dibasic acids areemployed, such as o-phthalic acid, isophthalic acid, terephthalic acid,homophthalic acid, 4,4- diphenyldicarboxylicacid, p,pdicarboxydiphenyl'sulfone, naphthalene-1,S-dicarboxylic acid,p-carboxyphenoxyacetic acid, etc.

In the first stage of the reaction, in accordance with the presentprocess, temperatures within the range of 90 to 160 C. may be employed.In the second stage, the mass is heated above the melting point thereof,which will vary with the nature of the polymer or intermediate productobtained. The temperature is maintained throughout the second stage at apoint sufliciently high to maintain a molten mass in the reactionvessel.

if desired, as pointed out hereinbefore, esterification catalysts may beemployed in the first stage, such as p-toluenesulfonic acid,camphor-sulfonic acid, and the like.

The polyesters of the instant invention have a different structure thanthose formed heretofore from aromatic dibasic acids and glycols, such asethylene glycol, as borne out by the lower melting points thereof.Sulfur analysis of the polymers produced has shown that the same aremodified with recurring structural units in amounts ranging from 0.5% toof the formula wherein R is the dibasic acid residue, such as 0-o c-oand the like, and R is ethylene or propylene.

, Further details of the present invention are set forth in thefollowing specific examples, which are merely intended to beillustrative and not limitative. Unless otherwise indicated, all partsand percents are by weight.

Example I A mixture of 3.0 grams of terephthalic acid, which had beenrecrystallized from N,N-dimethylacetamide, and 3.9 grams of ethylenesulfite Was heated to a temperature of 150 C. in a glass reaction vesselset in a liquid heating bath. After heating at 150 C. for minutes, aclear solution was obtained. Sulfur dioxide was evolved during thisstep. Thereafter the temperature was raised to 255 C. with slowintroduction of nitrogen to the reac tion vessel at one mm. pressure. Amelt having a viscosity of approximately 1000 poises at 255 C. wasobtained. Upon cooling the melt, an amorphous polymer, which wasessentially polyethylene terephthalate, was obtained. The polymer alsocontained 1.28 percent sulfur. Upon the belief that undecomposed sulfitegroups were present in the polymer, a sample was analyzed and thepolymer was found to contain 10% recurring units or one unit in ten, ofthe structure:

fite is increased in the presence of an alkaline substance;

Accordingly, the increased activity observed in Example I" was probablydue to the presence of an amine derived Example 11 A mixture of 2 gramsof terephthalic acid, which had been recrystallized fromN-methylpyrrolidone, and 5 grams of ethylene sulfite was heated in aglass reaction vessel set in a bath of methyl salicylate at 222 C. Theethylene sulfite was replenished as a portion distilled out to keep aconstant volume over an eight hour period. At the end of this time 0.05gram of undissolved terephthalic acid was removed by hot decantation. Tothe reacted portion, 0.005 gram of zinc acetate catalyst was added andthe temperature was raised to 280 C. with nitrogen introduction. Rapidpolymerization occurred. After a period of 4 hour a melt of 1200 poisesresulted. The polymer possessed a softening point of 70-75 C. andcrystallized at 100 C. on a Johns melting-point block. It subsequentlymelted sharply at 189 -190 C.

-A slight tendency to crystallize was noted on slow cooling to roomtemperature. Sulfur analysis indicated very few recurring structuralunits as defined in Example I. Fibers were drawn from the polymer meltwhich were soft, lustrous, and slightly brittle. The fibers possessedabout 50% elongation.

Example III A mixture of 5 grams of p,p-dicarboxybiphenyl and 6 grainsof ethylene sulfite was heated at 222 C. for 4 hours, as outlined inExample I, and then ethylene glycol was removed by distillation. A darkbrown, crystalline polyester which softened at C. and melted at 110 C.was obtained, 7

Example IV Using the procedure of Example III, terephthalic acid wascondensed with propylene sulfite. Polypropylene terephthalate, modifiedwith ethylene sulfite, was obtained which had a melting point below C.

The synthetic linear condensation polyesters, produced in accordancewith the instant process, while having their greatest utility in thefilament-and fiber-forming art, are also particularly adapted to moldingapplications. The filaments may be formed by extrusion or by drawingdirectly from the polymer melt after the completion of the heating(second stage) or after remelting, if desired. Any suitable apparatusmay be employed in forming the fibers and filaments. The polyesters ofthe instant invention are more plastic and accordingly filaments can bedrawn therefrom at lower temperatures.

Filaments, produced from the polyesters prepared in accordance with thepresent invention, can be cold-drawn to as much as several times theiroriginal lengths. They have greater elongation and are more elastic.These cold-drawing operations may be carried out on filaments, whichhave been allowed to cool fully and solidify, or the cold-drawing mayfollow the formation of the filaments directly as one part of acontinuous process. In this regard, it should also be pointed out thatthe instant process lends itself to continuous operation due to thegreat decrease in time to effect condensation or production of thepolyesters over processes employed heretofore.

In the cold-drawing operation any suitable apparatus and process may beused. For example, the filaments may be wound from one roller to anotherwith the second roller rotating at a higher speed than the firstroller.For example, the second roller may be rotated at a speed up to aboutfour or five times that of the first roller. If desired, cold-drawingmay be effected by employing a snubbing pin.

The term cold-drawing, as used herein, includes, in addition to drawingfilaments at temperatures as low as 0 C., warming the filaments tofacilitate stretching, for example, by passing the filaments throughwarm or hot water or steam before and/or during the cold-drawingoperation, or drawing the filaments at any temperature below the meltingpoint thereof.

Further, highly polymeric linear esters obtained according to theprocess of the present invention may be formed into other useful shapedarticles. For example, the melt of the highly polymeric linear polyestermay be formed into films and moldings by conventional procedures andapparatus. In addition, the polyesters may be used for hot melt coatingsor as adhesives, plasticizers, binders for coating compositions orbonding materials for laminated fabrics.

It is to be understood that changes and variations may be made withoutdeparting from the spirit and scope of the invention as defined in theappended claims.

I claim:

I. In the manufacture of synthetic linear condensation sulfur-containingpolyesters the steps comprising, forming a mixture of an aromaticdicarboxylic acid and a compound selected from the group consisting ofethylene sulfite and propylene sulfite, said components being present inthe mixture in a molar ratio of one mole of acid to 1 to 9 moles of thecompound, heating and reacting said mixture at a temperature in therange of 90 to 160 C. until no more sulfur dioxide is evolved, andthereafter continuing the heating at a temperature suificient tomaintain the reaction mass in a molten state until a sulfur-containingpolyester is produced.

2. The process defined in claim 1 wherein the compound is ethylenesulfite.

3. The process defined in claim 1 wherein the compound is propylenesulfite.

4. The process defined in claim 1 wherein the dicarboxylic acid isterephthalic acid.

5. The process defined in claim 1 wherein the dicarboxylic acid isisophthalic acid.

6. The process defined in claim 1 wherein the dicarboxylic acid is4,4-diphenyldicarboxylic acid.

7. The process defined in claim 1 wherein the dicar boxylic acid isterephthalic acid and the compound is ethylene sulfite.

8. The process defined in claim 7 wherein the molar ratio ofterephthalic acid to ethylene sulfite is one mole terephthalic acid toabout 2 to 4 moles of ethylene sulfite.

9. Synthetic linear condensation sulfur containing polyesters producedin accordance with the process of claim 1 and containing from 0.5 to 20%of recurring structural units of the formula:

produced in acproduced in ac produced in accordance with the process ofclaim 7.

16. The sulfur-containing polyesters formed in accordance with theprocess of claim 8 and containing from 0.5% to 20% recurring structuralunits of the formula:

References Cited in the file of this patent UNITED STATES PATENTSCarlson Sept. 7, 1948 Whinfield et al. Mar. 22, 1949

1. IN THE MANUFACTURE OF SYNTHETIC LINEAR CONDENSATION SULFUR-CONTAININGPOLYESTERS THE STEPS COMPRISING, FORMING A MIXTURE OF AN AROMATICDICARBOXYLIC ACID AND A COMPOUND SELECTED FROM THE GROUP CONSISTING OFETHYLENE SULFITE AND PROPLENE SULFITE, SAID COMPONENTS BEING PRESENT INTHE MIXTURE IN A MOLAR RATIO OF ONE MOLE OF ACID TO 1 TO 9 MOLES OF THECOMPOUND, HEATING AND REACTING SAID MIXTURE AT A TEMPERATURE IN THERANGE OF 90* TO 160*C. UNTIL NO MORE SULFUR DIOXIDE IS ENOLVED, ANDTHEREAFTER CONTINUING THE HEATING AT A TEMPERATURE SUFFICIENT TOMAINTAIN THE REACTION MASS IN A MOLTEN STATE UNTIL A SULFUR-CONTAININGPOLYESTER IS PRODUCED